The present invention relates to an apparatus for inspecting a fluorescent substance coated on a plasma display panel or a cathode-ray tube by image processing, that is used in a fluorescent substance coating step for the manufacture of plasma display panels or cathode-ray tubes.
Expectations are mounting that plasma displays can serve as large-scale high-precision displays for the coming multimedia age. Thus, suitable quality control at each step of the manufacturing process is becoming increasingly important, in addition to the efforts at reduction of the product costs. Most importantly, color mixing of red (R), green (G) and blue (B) must be quantitatively inspected after the fluorescent substances for light emission of each color have been coated on a panel. Accordingly, a speedy, highly reliable inspection method that can be performed in an in-line system is desirable with regard to mass-production of the plasma display.
A conventional inspection method of fluorescent substances on a plasma display panel is described below with reference to FIGS. 7 and 8.
In FIG. 7, a panel 32 that has been coated with fluorescent substances to be inspected is placed on a positioning table 31. An UV light illumination device 34 is provided for causing a fluorescent substance coating portion 33 on the panel 32 to emit light. A color TV camera 36 and a lens 37 are mounted as a set to a movable TV camera support portion 35. The color TV camera 36 is controlled by a color TV camera controller 38.
The image signals input from the color TV camera 36 are converted into numerical data representing, for example, 256 density levels in accordance with the density of the RGB image through an analog-digital converter 39, and input into an image processing unit 55 including a CPU, a ROM, a RAM and an I/O device.
The image processing unit 55 comprises an evaluation control unit (CPU) 40 to which commands are given from a main controller or a control panel, a processing area setting unit 41 for specifying the area to be processed, a color extraction unit 42 for extracting a certain color space in the processing area, a thresholding unit 43 for performing threshold processing based on the intensity in the extracted color space and for extracting a specific region of the image, an evaluation unit 44 for judging whether the fluorescent substance has been coated over a predetermined area, and a display/command unit 45 for displaying the detected results as, for example, acceptable or unacceptable, or displaying the results as images on a display of a computer terminal, and displaying the positions where a deficiency exists. The operation of an apparatus for inspecting the fluorescent substances on a plasma display panel with the above configuration is described below with reference to FIG. 8.
First, a panel 32 to be inspected is placed on the positioning table 31, and UV light is irradiated from the UV illumination device 34 to cause the fluorescent substance 33 to emit light. The light emitted by the fluorescent substance passes the lens 37 and is picked up by the color TV camera 36. The resulting image is converted into numerical data by the A/D converter 39, and input into the image processing unit 55 (step 1). Next, an area to be processed in the input image data is designated as the processing area (step 2), and a specific color is extracted from the image data in this processing area, wherein thresholding is performed (step 3). At step 4, characteristic features of the specified color area are extracted by measuring the area or other properties. Based on a comparison of these characteristic features with a registered reference value, the acceptability of the specified area is judged (step 5). If any defect is detected, such is displayed individually on the display of a computer terminal or the like, wherein the type of the deficiencies is indicated together with the detected location of these deficiencies (step 6).
However, because this inspection apparatus uses a regular color TV camera, the wavelength of the light emitted by the fluorescent substance cannot be converted precisely into RGB data, and it is difficult to identify delicate color mixing with high reliability. Furthermore, fast inspections that are suitable for in-line examination are difficult to realize.
It is therefore an object of the present invention to solve these and other problems of the related art and to provide an apparatus for inspecting the coating of a fluorescent substance on a plasma display panel, in which an examination of color mixing among PDP fluorescent substances is performed reliably and fast.
In order to attain these objects, an apparatus for inspecting the coating of a fluorescent substance on a plasma display panel in accordance with the present invention comprises:
a table on which a panel to be inspected, coated with a fluorescent substance is placed;
an illumination device for irradiating UV light onto the fluorescent substance for causing the fluorescent substance to emit light;
an imaging device for picking up an image of light emission of the fluorescent substance; and
a filter provided between the imaging device and the panel, that lets only light of specified wavelengths in accordance with light emission characteristics of the fluorescent substance pass toward the imaging device.
According to the present invention, a filter is provided that lets only light of certain wavelengths depending on light emission characteristics of the fluorescent substance pass toward the pick-up unit, so that a highly sensitive optical system adjusted to the light emission characteristics of the fluorescent substance can be realized, and even delicate color mixing can be detected with high reliability.
The apparatus is further provided with a visible rays cutting filter that prevents direct irradiation of visible light from the illumination device into the imaging device, so that, visible light, which tends to cause difficulties when inspecting the emission colors of the fluorescent substances, can be reduced.
The illumination device comprises a mirror for focusing the UV light emitted radially from a light source at a position at a certain distance, so that the fluorescent substances of the PDP are caused to emit strongly by illumination from a constant distance.
The apparatus is further provided with a mechanism for decreasing oxygen concentration of an atmosphere at the location where UV light is irradiated by the illumination device onto the fluorescent substance below the oxygen density in air, so that attenuation of UV light is prevented, that is brought about by the absorption of UV light due to the oxygen.
The imaging device comprises photodetectors arranged in a line, and the coating of the fluorescent substance is inspected continuously by moving the imaging device relatively to a direction that is perpendicular to a direction in which the photodetectors are arranged. The apparatus further comprises a unit for individually thresholding signals that are input from the photodetectors, and a unit for checking for deficiency candidates based on run lengths, which are detected by the unit for thresholding.
While novel features of the invention are set forth in the preceding, the invention, both as to organization and content, can be further understood and appreciated, along with other objects and features thereof, from the following detailed description and examples when taken in conjunction with the attached drawings.